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author | Mauro Carvalho Chehab <mchehab@s-opensource.com> | 2016-07-27 11:32:31 +0200 |
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committer | Mauro Carvalho Chehab <mchehab@s-opensource.com> | 2016-07-29 01:08:19 +0200 |
commit | 43f71d93a0cb342f0c918fba3f6abb7661e40ad2 (patch) | |
tree | a1dc7288bc480e7027ca1827ca4876472fa12e40 /Documentation/DocBook/media/v4l/dev-raw-vbi.xml | |
parent | Merge tag 'media/v4.8-4' of git://git.kernel.org/pub/scm/linux/kernel/git/mch... (diff) | |
download | linux-43f71d93a0cb342f0c918fba3f6abb7661e40ad2.tar.xz linux-43f71d93a0cb342f0c918fba3f6abb7661e40ad2.zip |
doc-rst: Remove the media docbook
Now that all media documentation was converted to Sphinx, we
should get rid of the old DocBook one, as we don't want people
to submit patches against the old stuff.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Diffstat (limited to 'Documentation/DocBook/media/v4l/dev-raw-vbi.xml')
-rw-r--r-- | Documentation/DocBook/media/v4l/dev-raw-vbi.xml | 345 |
1 files changed, 0 insertions, 345 deletions
diff --git a/Documentation/DocBook/media/v4l/dev-raw-vbi.xml b/Documentation/DocBook/media/v4l/dev-raw-vbi.xml deleted file mode 100644 index 78599bbd58f7..000000000000 --- a/Documentation/DocBook/media/v4l/dev-raw-vbi.xml +++ /dev/null @@ -1,345 +0,0 @@ - <title>Raw VBI Data Interface</title> - - <para>VBI is an abbreviation of Vertical Blanking Interval, a gap -in the sequence of lines of an analog video signal. During VBI -no picture information is transmitted, allowing some time while the -electron beam of a cathode ray tube TV returns to the top of the -screen. Using an oscilloscope you will find here the vertical -synchronization pulses and short data packages ASK -modulated<footnote><para>ASK: Amplitude-Shift Keying. A high signal -level represents a '1' bit, a low level a '0' bit.</para></footnote> -onto the video signal. These are transmissions of services such as -Teletext or Closed Caption.</para> - - <para>Subject of this interface type is raw VBI data, as sampled off -a video signal, or to be added to a signal for output. -The data format is similar to uncompressed video images, a number of -lines times a number of samples per line, we call this a VBI image.</para> - - <para>Conventionally V4L2 VBI devices are accessed through character -device special files named <filename>/dev/vbi</filename> and -<filename>/dev/vbi0</filename> to <filename>/dev/vbi31</filename> with -major number 81 and minor numbers 224 to 255. -<filename>/dev/vbi</filename> is typically a symbolic link to the -preferred VBI device. This convention applies to both input and output -devices.</para> - - <para>To address the problems of finding related video and VBI -devices VBI capturing and output is also available as device function -under <filename>/dev/video</filename>. To capture or output raw VBI -data with these devices applications must call the &VIDIOC-S-FMT; -ioctl. Accessed as <filename>/dev/vbi</filename>, raw VBI capturing -or output is the default device function.</para> - - <section> - <title>Querying Capabilities</title> - - <para>Devices supporting the raw VBI capturing or output API set -the <constant>V4L2_CAP_VBI_CAPTURE</constant> or -<constant>V4L2_CAP_VBI_OUTPUT</constant> flags, respectively, in the -<structfield>capabilities</structfield> field of &v4l2-capability; -returned by the &VIDIOC-QUERYCAP; ioctl. At least one of the -read/write, streaming or asynchronous I/O methods must be -supported. VBI devices may or may not have a tuner or modulator.</para> - </section> - - <section> - <title>Supplemental Functions</title> - - <para>VBI devices shall support <link linkend="video">video -input or output</link>, <link linkend="tuner">tuner or -modulator</link>, and <link linkend="control">controls</link> ioctls -as needed. The <link linkend="standard">video standard</link> ioctls provide -information vital to program a VBI device, therefore must be -supported.</para> - </section> - - <section> - <title>Raw VBI Format Negotiation</title> - - <para>Raw VBI sampling abilities can vary, in particular the -sampling frequency. To properly interpret the data V4L2 specifies an -ioctl to query the sampling parameters. Moreover, to allow for some -flexibility applications can also suggest different parameters.</para> - - <para>As usual these parameters are <emphasis>not</emphasis> -reset at &func-open; time to permit Unix tool chains, programming a -device and then reading from it as if it was a plain file. Well -written V4L2 applications should always ensure they really get what -they want, requesting reasonable parameters and then checking if the -actual parameters are suitable.</para> - - <para>To query the current raw VBI capture parameters -applications set the <structfield>type</structfield> field of a -&v4l2-format; to <constant>V4L2_BUF_TYPE_VBI_CAPTURE</constant> or -<constant>V4L2_BUF_TYPE_VBI_OUTPUT</constant>, and call the -&VIDIOC-G-FMT; ioctl with a pointer to this structure. Drivers fill -the &v4l2-vbi-format; <structfield>vbi</structfield> member of the -<structfield>fmt</structfield> union.</para> - - <para>To request different parameters applications set the -<structfield>type</structfield> field of a &v4l2-format; as above and -initialize all fields of the &v4l2-vbi-format; -<structfield>vbi</structfield> member of the -<structfield>fmt</structfield> union, or better just modify the -results of <constant>VIDIOC_G_FMT</constant>, and call the -&VIDIOC-S-FMT; ioctl with a pointer to this structure. Drivers return -an &EINVAL; only when the given parameters are ambiguous, otherwise -they modify the parameters according to the hardware capabilities and -return the actual parameters. When the driver allocates resources at -this point, it may return an &EBUSY; to indicate the returned -parameters are valid but the required resources are currently not -available. That may happen for instance when the video and VBI areas -to capture would overlap, or when the driver supports multiple opens -and another process already requested VBI capturing or output. Anyway, -applications must expect other resource allocation points which may -return <errorcode>EBUSY</errorcode>, at the &VIDIOC-STREAMON; ioctl -and the first read(), write() and select() call.</para> - - <para>VBI devices must implement both the -<constant>VIDIOC_G_FMT</constant> and -<constant>VIDIOC_S_FMT</constant> ioctl, even if -<constant>VIDIOC_S_FMT</constant> ignores all requests and always -returns default parameters as <constant>VIDIOC_G_FMT</constant> does. -<constant>VIDIOC_TRY_FMT</constant> is optional.</para> - - <table pgwide="1" frame="none" id="v4l2-vbi-format"> - <title>struct <structname>v4l2_vbi_format</structname></title> - <tgroup cols="3"> - &cs-str; - <tbody valign="top"> - <row> - <entry>__u32</entry> - <entry><structfield>sampling_rate</structfield></entry> - <entry>Samples per second, i. e. unit 1 Hz.</entry> - </row> - <row> - <entry>__u32</entry> - <entry><structfield>offset</structfield></entry> - <entry><para>Horizontal offset of the VBI image, -relative to the leading edge of the line synchronization pulse and -counted in samples: The first sample in the VBI image will be located -<structfield>offset</structfield> / -<structfield>sampling_rate</structfield> seconds following the leading -edge. See also <xref linkend="vbi-hsync" />.</para></entry> - </row> - <row> - <entry>__u32</entry> - <entry><structfield>samples_per_line</structfield></entry> - <entry></entry> - </row> - <row> - <entry>__u32</entry> - <entry><structfield>sample_format</structfield></entry> - <entry><para>Defines the sample format as in <xref -linkend="pixfmt" />, a four-character-code.<footnote> - <para>A few devices may be unable to -sample VBI data at all but can extend the video capture window to the -VBI region.</para> - </footnote> Usually this is -<constant>V4L2_PIX_FMT_GREY</constant>, i. e. each sample -consists of 8 bits with lower values oriented towards the black level. -Do not assume any other correlation of values with the signal level. -For example, the MSB does not necessarily indicate if the signal is -'high' or 'low' because 128 may not be the mean value of the -signal. Drivers shall not convert the sample format by software.</para></entry> - </row> - <row> - <entry>__u32</entry> - <entry><structfield>start</structfield>[2]</entry> - <entry>This is the scanning system line number -associated with the first line of the VBI image, of the first and the -second field respectively. See <xref linkend="vbi-525" /> and -<xref linkend="vbi-625" /> for valid values. -The <constant>V4L2_VBI_ITU_525_F1_START</constant>, -<constant>V4L2_VBI_ITU_525_F2_START</constant>, -<constant>V4L2_VBI_ITU_625_F1_START</constant> and -<constant>V4L2_VBI_ITU_625_F2_START</constant> defines give the start line -numbers for each field for each 525 or 625 line format as a convenience. -Don't forget that ITU line numbering starts at 1, not 0. -VBI input drivers can return start values 0 if the hardware cannot -reliable identify scanning lines, VBI acquisition may not require this -information.</entry> - </row> - <row> - <entry>__u32</entry> - <entry><structfield>count</structfield>[2]</entry> - <entry>The number of lines in the first and second -field image, respectively.</entry> - </row> - <row> - <entry spanname="hspan"><para>Drivers should be as -flexibility as possible. For example, it may be possible to extend or -move the VBI capture window down to the picture area, implementing a -'full field mode' to capture data service transmissions embedded in -the picture.</para><para>An application can set the first or second -<structfield>count</structfield> value to zero if no data is required -from the respective field; <structfield>count</structfield>[1] if the -scanning system is progressive, &ie; not interlaced. The -corresponding start value shall be ignored by the application and -driver. Anyway, drivers may not support single field capturing and -return both count values non-zero.</para><para>Both -<structfield>count</structfield> values set to zero, or line numbers -outside the bounds depicted in <xref linkend="vbi-525" /> and <xref - linkend="vbi-625" />, or a field image covering -lines of two fields, are invalid and shall not be returned by the -driver.</para><para>To initialize the <structfield>start</structfield> -and <structfield>count</structfield> fields, applications must first -determine the current video standard selection. The &v4l2-std-id; or -the <structfield>framelines</structfield> field of &v4l2-standard; can -be evaluated for this purpose.</para></entry> - </row> - <row> - <entry>__u32</entry> - <entry><structfield>flags</structfield></entry> - <entry>See <xref linkend="vbifmt-flags" /> below. Currently -only drivers set flags, applications must set this field to -zero.</entry> - </row> - <row> - <entry>__u32</entry> - <entry><structfield>reserved</structfield>[2]</entry> - <entry>This array is reserved for future extensions. -Drivers and applications must set it to zero.</entry> - </row> - </tbody> - </tgroup> - </table> - - <table pgwide="1" frame="none" id="vbifmt-flags"> - <title>Raw VBI Format Flags</title> - <tgroup cols="3"> - &cs-def; - <tbody valign="top"> - <row> - <entry><constant>V4L2_VBI_UNSYNC</constant></entry> - <entry>0x0001</entry> - <entry><para>This flag indicates hardware which does not -properly distinguish between fields. Normally the VBI image stores the -first field (lower scanning line numbers) first in memory. This may be -a top or bottom field depending on the video standard. When this flag -is set the first or second field may be stored first, however the -fields are still in correct temporal order with the older field first -in memory.<footnote> - <para>Most VBI services transmit on both fields, but -some have different semantics depending on the field number. These -cannot be reliable decoded or encoded when -<constant>V4L2_VBI_UNSYNC</constant> is set.</para> - </footnote></para></entry> - </row> - <row> - <entry><constant>V4L2_VBI_INTERLACED</constant></entry> - <entry>0x0002</entry> - <entry>By default the two field images will be passed -sequentially; all lines of the first field followed by all lines of -the second field (compare <xref linkend="field-order" /> -<constant>V4L2_FIELD_SEQ_TB</constant> and -<constant>V4L2_FIELD_SEQ_BT</constant>, whether the top or bottom -field is first in memory depends on the video standard). When this -flag is set, the two fields are interlaced (cf. -<constant>V4L2_FIELD_INTERLACED</constant>). The first line of the -first field followed by the first line of the second field, then the -two second lines, and so on. Such a layout may be necessary when the -hardware has been programmed to capture or output interlaced video -images and is unable to separate the fields for VBI capturing at -the same time. For simplicity setting this flag implies that both -<structfield>count</structfield> values are equal and non-zero.</entry> - </row> - </tbody> - </tgroup> - </table> - - <figure id="vbi-hsync"> - <title>Line synchronization</title> - <mediaobject> - <imageobject> - <imagedata fileref="vbi_hsync.pdf" format="PS" /> - </imageobject> - <imageobject> - <imagedata fileref="vbi_hsync.gif" format="GIF" /> - </imageobject> - <textobject> - <phrase>Line synchronization diagram</phrase> - </textobject> - </mediaobject> - </figure> - - <figure id="vbi-525"> - <title>ITU-R 525 line numbering (M/NTSC and M/PAL)</title> - <mediaobject> - <imageobject> - <imagedata fileref="vbi_525.pdf" format="PS" /> - </imageobject> - <imageobject> - <imagedata fileref="vbi_525.gif" format="GIF" /> - </imageobject> - <textobject> - <phrase>NTSC field synchronization diagram</phrase> - </textobject> - <caption> - <para>(1) For the purpose of this specification field 2 -starts in line 264 and not 263.5 because half line capturing is not -supported.</para> - </caption> - </mediaobject> - </figure> - - <figure id="vbi-625"> - <title>ITU-R 625 line numbering</title> - <mediaobject> - <imageobject> - <imagedata fileref="vbi_625.pdf" format="PS" /> - </imageobject> - <imageobject> - <imagedata fileref="vbi_625.gif" format="GIF" /> - </imageobject> - <textobject> - <phrase>PAL/SECAM field synchronization diagram</phrase> - </textobject> - <caption> - <para>(1) For the purpose of this specification field 2 -starts in line 314 and not 313.5 because half line capturing is not -supported.</para> - </caption> - </mediaobject> - </figure> - - <para>Remember the VBI image format depends on the selected -video standard, therefore the application must choose a new standard or -query the current standard first. Attempts to read or write data ahead -of format negotiation, or after switching the video standard which may -invalidate the negotiated VBI parameters, should be refused by the -driver. A format change during active I/O is not permitted.</para> - </section> - - <section> - <title>Reading and writing VBI images</title> - - <para>To assure synchronization with the field number and easier -implementation, the smallest unit of data passed at a time is one -frame, consisting of two fields of VBI images immediately following in -memory.</para> - - <para>The total size of a frame computes as follows:</para> - - <programlisting> -(<structfield>count</structfield>[0] + <structfield>count</structfield>[1]) * -<structfield>samples_per_line</structfield> * sample size in bytes</programlisting> - - <para>The sample size is most likely always one byte, -applications must check the <structfield>sample_format</structfield> -field though, to function properly with other drivers.</para> - - <para>A VBI device may support <link - linkend="rw">read/write</link> and/or streaming (<link - linkend="mmap">memory mapping</link> or <link - linkend="userp">user pointer</link>) I/O. The latter bears the -possibility of synchronizing video and -VBI data by using buffer timestamps.</para> - - <para>Remember the &VIDIOC-STREAMON; ioctl and the first read(), -write() and select() call can be resource allocation points returning -an &EBUSY; if the required hardware resources are temporarily -unavailable, for example the device is already in use by another -process.</para> - </section> |